S-alkyl Cysteine Research Articles

Identification and analysis of NAC genes related to S-alk(en)yl cysteine sulfoxides (CSOs) biosynthesis in Onion (Allium cepa L.)

The NAC family, a specific type of plant transcription factor, has been identified in various horticultural crops. Nevertheless, the comprehensive bioinformatics and biological function of the NAC family in onion remain unclear. S-alk(en)yl cysteine sulfoxides (CSOs) are crucial for onion flavor quality and health effects. There is a growing interest in studying the mechanism of CSOs synthesis regulation in onions due to the increased realization of their potential value. In this study, sixty members of the NAC family was identified based on transcriptomic data. These transcription factors were distributed on eight chromosomes of onion. Phylogenetic tree showed that AcNAC members were divided into three groups with similar conserved protein motifs. Cis-acting elements analysis showed that the promoter of AcNACs contained a large number of photoresponsive and hormone-responsive elements. The correlation analysis of the expression patterns of transcriptome data selected 18 AcNACs that might regulate the synthesis of CSOs. Two putative NAC transcription factors, AcNAC12 and AcNAC17, were speculated as potential regulators in the biosynthesis of CSOs in onions through the analysis of expression patterns of AcNAC genes across different growth stages and cultivars, as well as Y1H, dual luciferase, GUS staining, and gene suppression experiments. This study aims to provide suggestions and research directions for further investigation of the functions of AcNAC family members and regulatory pathways for CSO biosynthesis.

Effects of blanching cultivation on the chemical composition and nutritional quality of Chinese chive

Blanching is an agricultural practice where vegetables are cultivated in darkness to prevent photosynthesis, thereby modifying their colour, texture, and flavor. The technique is popularly employed in Chinese chive (CC). Blanched Chinese chive (BCC) is renowned for its pale-yellow appearance, delicate flavor, and culinary-medicinal values; nonetheless, how blanching alters the chemical composition largely remains intangible. In this study, the physiological, nutritional, and metabolic profiles of BCC and CC were investigated. In BCC, the contents of ascorbic acid, flavonoids, anthocyanins, etc. were decreased markedly, whereas the sugar content and pungency were increased significantly, indicating that blanching shaped the vegetable flavor. UPLC-ESI-MS/MS analysis revealed 366 differential metabolites between BCC and CC, and the metabolism of flavor precursors, S-alk(en)yl cysteine sulfoxides, were stimulated by blanching. Together, these findings give a strong clue that blanching increases the pungency flavor in CC, and is a useful technique for other selected vegetables.

Characterization of phytochemicals from twisted-leaf garlic (Allium obliquum L.) using liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry

IntroductionTwisted-leaf garlic (Allium obliquum L.) is a wild Allium species, which is traditionally used as aroma plant for culinary purposes due to its unique, garlic-like flavor. It represents an interesting candidate for domestication, breeding and cultivation.ObjectivesThe objective of this work was to explore and comprehensively characterize polar and semi-polar phytochemicals accumulating in leaves and bulbs of A. obliquum.MethodPlant material obtained from a multiyear field trial was analyzed using a metabolite profiling workflow based on ultra-high performance liquid chromatography-coupled electrospray ionization quadrupole time-of-flight mass spectrometry (UHPLC/ESI-QTOFMS) and two chromatographic methods. For annotation of metabolites, tandem mass spectrometry experiments were carried out and the resulting accurate-mass collision-induced dissociation (CID) mass spectra interpreted. Onion and garlic bulb extracts were used as reference samples.ResultsImportant metabolite classes influencing nutritional, sensory and technological properties were detected and structurally characterized including fructooligosaccharides with a degree of polymerization of 3–5, S-alk(en)ylcysteine sulfoxides and other S-substituted cysteine conjugates, flavonoids including O- and C-glycosylated flavones as well as O-glycosylated flavonols, steroidal saponins, hydroxycinnamic acid conjugates, phenylethanoids and free sphingoid bases. In addition, quantitative data for non-structural carbohydrates, S-alk(en)ylcysteine sulfoxides and flavonoids are provided.ConclusionThe compiled analytical data including CID mass spectra of more than 160 annotated metabolites provide for the first time a phytochemical inventory of A. obliquum and lay the foundation for its further use as aroma plant in food industry.

The dynamics of bioactive compounds and their contributions to the antioxidant activity of postharvest chive (Allium schoenoprasum L.)

Organosulfur compounds, phenolic compounds, and ascorbic acids (AsA) are known to account for the bulk of chive’s (Allium schoenoprasum L.) antioxidant properties. This study uncovered the contribution of each of these compounds to the chive's antioxidant activity under different storage conditions. The results showed that room temperature (RT) accelerated the accumulation of reactive oxygen species, though phenolics, organosulfur compounds, activities of antioxidant enzymes, and scavenging activity toward hydroxyl radical (OH) and superoxide anion (O2−) were observed to be enhanced in chives stored at RT. In contrast, AsA content, DPPH (1,1-diphenyl-1-picrylhydrazyl) scavenging and FRAP (ferric reducing antioxidant power) activity of the chive were increased by LT on day 5. Furthermore, S-alk(en)ylcysteine sulfoxides (CSOs) showed OH scavenging and weak DPPH scavenging but had no O2− scavenging and FRAP capacity. Volatile organosulfur compounds showed no antioxidant activities. Conclusively, the data demonstrated that AsA was largely responsible for DPPH scavenging and FRAP activity of the chive, while phenolic compounds, especially vanillic acid and p-hydroxybenzoic acid, were primarily responsible for OH and O2− scavenging activity.

Alkylcysteine Sulfoxide C-S Monooxygenase Uses a Flavin-Dependent Pummerer Rearrangement.

Flavoenzymes are highly versatile and participate in the catalysis of a wide range of reactions, including key reactions in the metabolism of sulfur-containing compounds. S-Alkyl cysteine is formed primarily by the degradation of S-alkyl glutathione generated during electrophile detoxification. A recently discovered S-alkyl cysteine salvage pathway uses two flavoenzymes (CmoO and CmoJ) to dealkylate this metabolite in soil bacteria. CmoO catalyzes a stereospecific sulfoxidation, and CmoJ catalyzes the cleavage of one of the sulfoxide C-S bonds in a new reaction of unknown mechanism. In this paper, we investigate the mechanism of CmoJ. We provide experimental evidence that eliminates carbanion and radical intermediates and conclude that the reaction proceeds via an unprecedented enzyme-mediated modified Pummerer rearrangement. The elucidation of the mechanism of CmoJ adds a new motif to the flavoenzymology of sulfur-containing natural products and demonstrates a new strategy for the enzyme-catalyzed cleavage of C-S bonds.

Isotope-Guided Metabolomics Reveals Divergent Incorporation of Valine into Different Flavor Precursor Classes in Chives.

Plants of the genus Allium such as chives, onions or garlic produce S-alk(en)yl cysteine sulfoxides as flavor precursors. Two major representatives are S-propenyl cysteine sulfoxide (isoalliin) and S-propyl cysteine sulfoxide (propiin), which only differ by a double bond in the C3 side chain. The propenyl group of isoalliin is derived from the amino acid valine, but the source of the propyl group of propiin remains unclear. Here, we present an untargeted metabolomics approach in seedlings of chives (Allium schoenoprasum) to track mass features containing sulfur and/or 13 C from labeling experiments with valine-13 C5 guided by their isotope signatures. Our data show that propiin and related propyl-bearing metabolites incorporate carbon derived from valine-13 C5 , but to a much lesser extent than isoalliin and related propenyl compounds. Our findings provide new insights into the biosynthetic pathways of flavor precursors in Allium species and open new avenues for future untargeted labeling experiments.

Metabolomics and transcriptomics analyses provides insights into S-alk(en)yl cysteine sulfoxides (CSOs) accumulation in onion (Allium cepa)

Primary and secondary metabolites are responsible for the nutritional value of onions. S-Alk(en)ylcysteine sulfoxides (CSOs) are the precursors of onion flavour and medicinal components. The purpose of this study was to investigate the dynamics in metabolites and CSOs biosynthesis during onion bulb expansion by conducting metabolomic and transcriptomic analyses. A total of 633 metabolites were detected in SA1. Lipids, flavonoids and amino acids mainly accumulated in the rapid-expansion stage of onion bulb, whereas alkaloids and phenolic acids accumulated in the late stage of bulb expansion. The concentration of S-methylcysteine sulfoxide (MCSO) was increased in SA1 during onion bulb development, however, there was no significant changes in S-propylcysteine sulfoxide (PeCSO) and S-allylcysteine sulfoxide (ACSO). Candidate genes involving in CSOs biosynthesis were screened by RNA-Seq. Two AcSULTRs and AcCSs, a AcATPS, AcSAT, AcGL, AcGS, AcGGT and AcFMO might play core roles in CSOs biosynthesis. The results offer a theoretical basis for determining the regulation of organosulfur compound synthesis in onion.

Physiological, transcriptomic, and metabolic analyses reveal that mild salinity improves the growth, nutrition, and flavor properties of hydroponic Chinese chive (Allium tuberosum Rottler ex Spr)

Environmental stressors such as salinity have pronounced impacts on the growth, productivity, nutrition, and flavor of horticultural crops, though yield loss sometimes is inevitable. In this study, the salinity influences were evaluated using hydroponic Chinese chive (Allium tuberosum) treated with different concentrations of sodium chloride. The results demonstrated that lower salinity could stimulate plant growth and yield. Accordingly, the contents of soluble sugar, ascorbic acid, and soluble protein in leaf tissues increased, following the decrease of the nitrate content, under mild salinity (6.25 or 12.5 mM NaCl). However, a higher level of salinity (25 or 50 mM NaCl) resulted in growth inhibition, yield reduction, and leaf quality deterioration of hydroponic chive plants. Intriguingly, the chive flavor was boosted by the salinity, as evidenced by pungency analysis of salinity-treated leaf tissues. UPLC-MS/MS analysis reveals that mild salinity promoted the accumulation of glutamic acid, serine, glycine, and proline in leaf tissues, and thereby enhanced the umami and sweet flavors of Chinese chive upon salinity stress. Considering the balance between yield and flavor, mild salinity could conduce to hydroponic Chinese chive cultivation. Transcriptome analysis revealed that enhanced pungency could be ascribed to a salt stress-inducible gene, AtuFMO1, associated with the biosynthesis of S-alk(en)yl cysteine sulphoxides (CSOs). Furthermore, correlation analysis suggested that two transcription factors, AtubHLH and AtuB3, were potential regulators of AtuFMO1 expressions under salinity. Thus, these results revealed the molecular mechanism underlying mild salinity-induced CSO biosynthesis, as well as a practical possibility for producing high-quality Chinese chive hydroponically.

S-alk(en)ylcysteine sulfoxides biosynthesis and free amino acids profile in different parts of postharvest chive (Allium schoenoprasum L.)

The purpose of this study was to investigate the dynamics in S-alk(en)ylcysteine sulfoxides (CSOs) biosynthesis and free amino acids (FAA) accumulation and remobilization in different parts of chive during postharvest storage. The chives were stored for 5 days at 20 °C (RT) and 20 days at 3 °C (LT). The CSOs and most of the FAA accumulated in the bottom-white part (BW) during chive senescence in the round-green part (RG) during the storage. There was a strong correlation (0.75<r<0.96, P<0.001) between the CSOs and FAA changes in the RG and the BW of the chive. In the BW of the chive, the total CSOs content increased by 17.53 % under RT and 38.06 % under LT storage, while the content of total FAA increased by 443 % under RT and 464 % during LT storage. However the CSOs and FAA changed much less in the RG of the chive during the storage. The FAA, glutathione S-transferase (GST) and γ-glutamyl dipeptidase (GGT) results further indicated that the CSOs were biosynthesized in whole parts but much higher in the BW part during storage. The product of proteolysis (Met and Ser) provided the material for the biosynthesis of CSOs via Cys the pathway. The change in the CSOs and FAA profile in RG and BW of chive during storage was through a source-to-sink transition phenomenon, which resulted in the remobilization of the nutrient (S and N) from the RG to BW parts of the chive. The LT storage increased CSOs accumulation by prolonging the storage time, delayed FAA accumulation by inhibiting proteolysis and increased protein content in the BW during the storage. Our study's results provide new insight into the CSOs biosynthesis of postharvest chive and the role of storage temperatures on S-alk(en)ylcysteine sulfoxides biosynthesis and FAA remobilization in postharvest chive.

Transcriptome analysis reveals the genes involved in S-alk(en)ylcysteine sulfoxide biosynthesis and its biosynthetic location in postharvest chive (Allium schoenoprasum L.)

The biosynthetic mechanism of S-alk(en)ylcysteine sulfoxides (CSOs), a flavor precursor and nonvolatile medicinal compound in chive is still poorly understood. In the present study, transcriptomic analysis was used to investigate the biosynthetic mechanism of S-alk(en)ylcysteine sulfoxides (CSOs) in green leaves of postharvest chive stored under normal temperature (20 °C) for 5 d and low-temperature (3 °C) for 12 d. The de novo assembly of the transcriptome enabled the identification of unigenes involved in the sulfur assimilation and CSOs biosynthesis. The RNA-seq data showed that the unigenes related to sulfur assimilation were down-regulated during storage under 20 °C and 3 °C. The low temperature did not affect cysteine biosynthesis and the expression of γ-glutamyl transpeptidase (GGT) and flavin-containing monooxygenase (FMO) involved in CSOs biosynthesis; nonetheless, it prolonged CSOs synthesis by sustaining the chive quality during the storage period. The qPCR data revealed that the expressions of genes related to sulfur assimilation were mainly in the white stalk. In contrast, CSOs biosynthetic genes had higher expression levels in green leaf. The results indicate the CSOs were mainly synthesized in green leaf while cysteine, the primary substrate for CSOs synthesis, was from de novo synthesis and proteolysis. The study presents discrete evidence that CSOs biosynthesis in postharvest chives occurs in green leaves and is translocated to the white stalk for storage.

The ability of callus tissues induced from three Allium plants to accumulate health-beneficial natural products, S-alk(en)ylcysteine sulfoxides

S-Alk(en)ylcysteine sulfoxides (CSOs), such as methiin, alliin, and isoalliin, are health-beneficial natural products biosynthesized in the genus Allium. Here, we report the induction of multiple callus tissue lines from three Allium vegetables, onion (A. cepa), Welsh onion (A. fistulosum), and Chinese chive (A. tuberosum), and their ability to accumulate CSOs. Callus tissues were initiated and maintained in the presence of picloram and 2-isopentenyladenine as auxin and cytokinin, respectively. For all plant species tested, the callus tissues almost exclusively accumulated methiin as CSO, while the intact plants contained a substantial amount of isoalliin together with methiin. These results suggest that the cellular developmental conditions and the regulatory mechanisms required for the biosynthesis of methiin are different from those of alliin and isoalliin. The methiin content in the callus tissues of onion and Welsh onion was much higher compared to that in the intact plants, and its cellular concentration could be estimated as 1.9–21.7 mM. The activity of alliinase that degrades CSOs in the callus tissues was much lower than that of the intact plants for onion and Welsh onion, but at similar levels as in the intact plants for Chinese chive. Our findings that the callus tissues of onion and Welsh onion showed high methiin content and low alliinase activity highlighted their potential as a plant-based system for methiin production.

Effect of Organosulfur Compounds from Different Garlic Preparations on Hyperlipidemia: An in-silico Approach

Garlic is one of the most well-known medicinal plants in terms of hypolipidemic activities. Its organosulfur compounds (OSCs) are probably one of the major groups of potentially active compounds for treating hyperlipidemia. However, the hypolipidemic activities of many garlic OCSs have not been investigated. This study was conducted to predict the potential of garlic OSCs to interact with hyperlipidemia targets and to evaluate their pharmacokinetic properties. 25 OSCs were selected to interact with four major targets of hyperlipidemia named pancreatic lipase, HMG-CoA reductase, PPAR-α, and NPC1L1 using the AutoDock Vina program. The pharmacokinetic properties of OSCs were also evaluated by the SwissADME website. The best binding affinity values were obtained for γ-glutamyl-S-alk(en)ylcysteines. Other OSCs, such as S-alk(en)ylcysteine sulfoxides and ajoenes, presented a moderate to high affinity for the studied targets. However, in-silico evaluation of pharmacokinetic properties showed that γ-glutamyl-S-alk(en)ylcysteines have low absorption. The results displayed that γ-glutamyl-S-alk(en)ylcysteines can potentially be considered antihyperlipidemic agents mainly influencing the intestinal lumen. Therefore, it seems that fresh whole garlic, thermal dehydrated garlic, and freeze-dried garlic products are probably more potent antihyperlipidemic agents due to their higher levels of γ-glutamyl-S-alk(en)ylcysteines.

1-Methylcyclopropene Preserves the Quality of Chive (Allium schoenoprasum L.) by Enhancing Its Antioxidant Capacities and Organosulfur Profile during Storage.

The quality, antioxidant capacities, and organosulfur profile of chives (Allium schoenoprasum L.) treated with 1-methylcyclopropene (1-MCP) during storage were investigated in this study. The 1-MCP treatment (100 μL/L, fumigation 12 h at 20 °C) effectively inhibited tissue respiration and H2O2 production, enhanced the ascorbic acid (ASA) and glutathione (GSH) content, and promoted the activity of antioxidant enzymes (superoxide dismutase SOD, Catalase CAT, and ascorbic peroxidase APX) during the 5-day storage period at 20 °C. The result further showed that the 1-MCP treatment inhibited chlorophyll degradation, alleviated cell membrane damage, and delayed the chive senescence, with the yellowing rate being reduced by 67.8% and 34.5% in the 1-MCP treated chives on days 4 and 5 of storage at 20 °C, respectively. The free amino acid content of the chive was not affected by the 1-MCP treatment at 20 °C. However, the senescence rate of the chive was not reduced by the 1-MCP treatment when stored at 3 °C. The liquid chromatography data further showed that the 1-MCP treatment induced a 15.3% and 13.9% increase in the isoalliin and total S-alk(en)ylcysteine sulfoxides (ACSOs) content of the chive on day 2 at 20 °C, respectively. Furthermore, there was a strong positive correlation between ACSOs content and CAT/APX activity, indicating that ACSOs probably played a key role in enhancing the antioxidant capacities of the chive during storage at 20 °C. Thus the study efficiently demonstrates that 1-methylcyclopropene preserves the quality of chive (Allium schoenoprasum L.) by enhancing its antioxidant capacities and organosulfur profile during storage.

Transcriptome landscapes of multiple tissues highlight the genes involved in the flavor metabolic pathway in Chinese chive (Allium tuberosum)

The unique flavor of Allium tuberosum is primarily associated with the hydrolysis of a series of organosulfur compounds, S-alk(en)yl cysteine sulphoxides (CSOs), upon tissue bruising or maceration. To obtain the tissue-specific transcriptomes, 18 RNA-Seq libraries representing leaf, root, stem, mature flower, inflorescence, and seed tissues of A. tuberosum were sequenced, finally yielding 133.7 Gb clean reads. The de novo assembled transcriptomes enabled the identification of 223,529 unigenes, which were functionally annotated and analyzed for the gene ontology and metabolic pathways. Furthermore, to reveal the flavor metabolic pathways, a total of 205 unigenes involved in the sulfur assimilation and CSO biosynthesis were identified, and their expression profiles were analyzed by RNA-Seq and qRT-PCR. Collectively, this study provides a valuable resource for in-depth molecular and functional researches especially on flavor formation, as well as for the development of molecular markers, and other genetic studies in A. tuberosum.

S-Alk(en)ylcysteine sulfoxides in the genus Allium: proposed biosynthesis, chemical conversion, and bioactivities.

S-Alk(en)ylcysteine sulfoxides are sulfur-containing natural products characteristic of the genus Allium. Both the flavor and medicinal properties of Allium plants are attributed to a wide variety of sulfur-containing compounds that are generated from S-alk(en)ylcysteine sulfoxides. Previous radiotracer experiments proposed that S-alk(en)ylcysteine sulfoxides are biosynthesized from glutathione. The recent identification of γ-glutamyl transpeptidases and a flavin-containing S-oxygenase involved in the biosynthesis of S-allylcysteine sulfoxide (alliin) in garlic (Allium sativum) provided insights into the reaction order of deglutamylation and S-oxygenation together with the localization of the biosynthesis, although the rest of the enzymes in the pathway still await discovery. In intact plants, S-alk(en)ylcysteine sulfoxides are stored in the cytosol of storage mesophyll cells. During tissue damage, the vacuolar enzyme alliinase contacts and hydrolyzes S-alk(en)ylcysteine sulfoxides to produce the corresponding sulfenic acids, which are further converted into various sulfur-containing bioactive compounds mainly via spontaneous reactions. The formed sulfur-containing compounds exhibit bioactivities related to pathogen defense, the prevention and alleviation of cancer and cardiovascular diseases, and neuroprotection. This review summarizes the current understanding of the occurrence, biosynthesis, and alliinase-triggered chemical conversion of S-alk(en)ylcysteine sulfoxides in Allium plants as well as the impact of S-alk(en)ylcysteine sulfoxides and their derivatives on medicinal, food, and agricultural sciences.

Radiolabeling and Preclinical Evaluation of a New S-Alkylated Cysteine Derivative Conjugated to C-Substituted Macrocycle for Positron Emission Tomography.

A new S-alkylated cysteine-derivatized tumor targeting agent, 2,2′-(12-(2-((2-acetamido-2-carboxyethyl)thio)acetamido)-11,13-dioxo-1,4,7,10-tetraazacyclotridecane-4,7-diyl)diacetic acid was developed for positron emission tomography (PET) imaging. N-Acetyl cysteine (NAC) was conjugated to ATRIDAT as a specific targeting agent toward L-type and ASC amino acid transporter systems in the oncogenic cells. NAC was attached via S-alkylation to prevent its incorporation at undesired recognition sites affecting the signal-to-noise ratio. NAC-ATRIDAT was subjected to gallium-68 complexation with >75% radiolabeling yield. The radiocomplex was purified through the tc18 cartridge to obtain 99.89% radiochemical yield. IC-50 of the NAC-ATRIDAT conjugate was 0.8 mM in A549 cells as evaluated through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazonium bromide assay. Binding affinity experiments on A549 cells showed noteworthy binding with KD in the nanomolar range. A time course study showed a Km value of 0.19 μM and Vmax value of 0.49 pmol/μg protein/min showing reasonable tumor kinetics. Efflux studies showed that the synthesized radioligand is transported majorly by LAT followed by the ASC system. Clearance was found to be renal with 7.67 ± 1.48% ID/g uptake at 30 min which substantially declined to 0.52 ± 0.% ID/g at 4 h. A significant uptake of 10.06 ± 1.056% ID/g was observed at the tumor site in mice at 1 h. μPET images revealed a high contrast with a tumor-to-kidney ratio of 4.8 and a tumor-to-liver ratio of 35.85 at 1 h after injection. These preclinical in vitro and in vivo evaluation supports its potential on the way of becoming a successful 68Ga-radiolabeled amino acid-based PET imaging agent.

Determination of bioactive compounds in ten cultivars of onions from Aragón and Castilla y León

Onion (Allium cepa L.) is one of the most important agricultural crops worldwide. The onion has high content of bioactive compounds and by this it is a food with healthy proprieties. The onion has two groups of compounds with these proprieties: S-alk(en)yl-cysteine sulphoxides (ACSOs), which are also flavour precursors, and non-sulfur compounds. In non-sulfur compounds, there are: flavonoids (mainly flavonols), fructans and saponins. Quercetin and its derivatives are the most important flavonols. Onion is an excellent source of quercetin, which is known to have various health benefits. The aim of this study was: cultivar selection according to the quantity of some bioactive compounds with healthy benefits. In this study, ten local onion landraces were supplied by the Vegetable Germplasm Bank in Zaragoza (BGHZ) Centro de Investigacion y Tecnologia Agroalimentaria (CITA) of Zaragoza (Spain), and these correspond to two Spanish autonomous communities: “Aragon” and “Castilla y Leon”. The ten onion cultivars were grown in a greenhouse (CITA) under the same conditions of time, temperature, climate, soil and nutrient supply. The samples were processed as follows: the two outer layers were removed (dry brown layers), cut and the central part were minced and frozen. The pyruvic acid content, total polyphenols, quercetin, antioxidant capacity, pH and soluble solids were evaluated. In relation to the pyruvic acid content in the different cultivars studied, it was found that all of them showed little pungency and can be classified as sweet. The cultivar ‘BGHZ-3096’ (“Cebolla Pequena”, Teruel) presented the highest content in total polyphenols, quercetin and antioxidant capacity, and the highest soluble solids content, of all the cultivars analyzed.

Comprehensive metabolite profiling of onion bulbs (Allium cepa) using liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry

Onion (Allium cepa) represents one of the most important horticultural crops and is used as food, spice and medicinal plant almost worldwide. Onion bulbs accumulate a broad range of primary and secondary metabolites which impact nutritional, sensory and technological properties. To complement existing analytical methods targeting individual compound classes this work aimed at the development and validation of an analytical workflow for comprehensive metabolite profiling of onion bulbs. Metabolite profiling was performed by liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (LC/ESI-QTOFMS). For annotation of metabolites accurate mass tandem mass spectrometry experiments were carried out. On the basis of LC/ESI-QTOFMS and two chromatographic methods an analytical workflow was developed which facilitates profiling of polar and semi-polar onion metabolites including fructooligosaccharides, proteinogenic amino acids, peptides, S-substituted cysteine conjugates, flavonoids and saponins. To minimize enzymatic conversion of S-alk(en)ylcysteine sulfoxides, a sample preparation and extraction protocol for fresh onions was developed comprising cryohomogenization and a low-temperature quenching step. A total of 123 metabolites were annotated and characterized by chromatographic and tandem mass spectral data. For validation, recovery rates and matrix effects were determined for 15 model compounds. Repeatability and linearity were assessed for more than 80 endogenous metabolites. As exemplarily demonstrated by comparative metabolic analysis of six onion cultivars the established analytical workflow in combination with targeted and non-targeted data analysis strategies can be successfully applied for comprehensive metabolite profiling of onion bulbs.

Gas-Phase Oxidation via Ion/Ion Reactions: Pathways and Applications.

Here, we provide an overview of pathways available upon the gas-phase oxidation of peptides and DNA via ion/ion reactions and explore potential applications of these chemistries. The oxidation of thioethers (i.e., methionine residues and S-alkyl cysteine residues), disulfide bonds, S-nitrosylated cysteine residues, and DNA to the [M+H+O]+ derivative via ion/ion reactions with periodate and peroxymono-sulfate anions is demonstrated. The oxidation of neutral basic sites to various oxidized structures, including the [M+H+O]+, [M-H]+, and [M-H-NH3]+ species, via ion/ion reactions is illustrated and the oxidation characteristics of two different oxidizing reagents, periodate and persulfate anions, are compared. Lastly, the highly efficient generation of molecular radical cations via ion/ion reactions with sulfate radical anion is summarized. Activation of the newly generated molecular radical peptide cations results in losses of various neutral side chains, several of which generate dehydroalanine residues that can be used to localize the amino acid from which the dehydroalanine was generated. The chemistries presented herein result in a diverse range of structures that can be used for a variety of applications, including the identification and localization of S-alkyl cysteine residues, the oxidative cleavage of disulfide bonds, and the generation of molecular radical cations from even-electron doubly protonated peptides. Graphical Abstract ᅟ.

Allium Roseum L. Extract Exerts Potent Suppressive Activities on Chronic Myeloid Leukemia K562 Cell Viability Through the Inhibition of BCR-ABL, PI3K/Akt, and ERK1/2 Pathways and the Abrogation of VEGF Secretion

ABSTRACTUse of plant extracts, alone or combined to the current chemotherapy as chemosensitizers, has emerged as a promising strategy to overcome tumor drug resistance. Here, we investigated the anticancer activity of Allium roseum L. extracts, a wild edible species in North Africa, on human Chronic Myeloid Leukemia (CML) K562 cells. The dehydrated aqueous extract (DAE) disturbed the cell cycle progression and induced the apoptosis of K562 cells. Chemical analysis of DAE showed a diversity of organosulfur compounds S-alk(en)yl-cysteine sulfoxides (RCSO) and high amount of allicin, suggesting that such molecule may be behind its antitumor effect. DAE was efficient in inhibiting K562 cell viability. DAE inhibitory effect was associated with the dephosphorylation of the BCR-ABL kinase and interfered with ERK1/2, Akt, and STAT5 pathways. Furthermore, we found that DAE-induced inactivation of Akt kinase led to the activation of its target FOXO3 transcription factor, enhancing the expression of FOXO3-regulated proapoptotic effectors, Bim and Bax, and cell cycle inhibitor p27. Finally, we found that DAE reduced the secretion of vascular endothelial growth factor. Overall, our data suggest that A. roseum extract has great potential as a nontoxic cheap and effective alternative to conventional chemotherapy.